Diaphragms used in brake actuators operated by fluid pressure, such as actuators in air braking systems of trucks and trains, are made from a layer of fabric, e.g., nylon, sandwiched between two layers of flexible material, generally rubber or synthetic rubber, to form an integral structure. The diaphragm generally is supported at its periphery within a housing of the actuator. Upon introduction of fluid pressure, such as compressed air, on one side of the diaphragm, the diaphragm moves a push plate or piston to actuate a braking mechanism. The diaphragm is returned to its normal position when the compressed air is released by a spring exerting an opposite force on the push plate or piston.
Diaphragms of this type generally are cup shaped with a bottom wall or base merging into a conical annular wall. The conical annular wall terminates at an annular lip or flange which is clamped between upper and lower portions of the housing.
In normal operation, a diaphragm of this type is inverted by the force of the compressed air, and returned to its normally biased position, many thousands of times. Such repeated motion places extreme stress on the diaphragm, often causing wear or rupture. In order to increase the life of diaphragms of this type, various spacing structures at the zone of merger between the diaphragm's bottom wall and annular sidewall have been proposed. See, e.g., U.S. Pat. Nos. 3,135,173; 3,435,734; 3,872,777; and 3,911,796. Although these structures may increase the life of the diaphragm, they also increase the cost, and the quantity of materials needed, for manufacture.